1. Field of the Invention
The present invention relates to a chemical vapor deposition (CVD) apparatus, and more particularly, to a chemical vapor deposition apparatus which uses radicals of reactant gases while supplying process gases in sequence by generating plasma within a showerhead or injecting exterior plasma into a chamber through the showerhead.
2. Description of the Prior Art
Generally, in order to obtain excellent step coverage and film quality characteristics at low temperature, source gases and reactant gases are supplied to a chemical vapor deposition apparatus in sequence. Herein, a conventional chemical vapor deposition apparatus in which process gases are sequentially supplied will be briefly described with reference to FIGS. 1A to 1C.
FIG. 1A is a schematic view showing constitutional elements of the conventional chemical vapor deposition apparatus in which the process gases are sequentially supplied. As shown in FIG. 1A, the conventional chemical vapor deposition apparatus comprises a chamber 101 with an outlet 100 disposed at a lower portion thereof, at least one source gas introduction tube 102 mounted on a top surface of the chamber so as to penetrate into an inner central portion of the chamber 101, at least one reactant gas introduction tube 103 and at least one purge gas introduction tube 104, a showerhead 106 with a plurality of injection holes 105 formed therein for injecting the process gases, and a heater 108 for supporting a wafer or substrate 107 (hereinafter, referred to as “substrate”) on which a thin film is deposited from the process gases injected through the showerhead 106 and for simultaneously functioning as a heat source.
In order to form the thin film on the substrate 107 by using the conventional chemical vapor deposition apparatus constructed as such, the source gases introduced from the at least one source gas introduction tube 102 are injected through the showerhead 106 for a predetermined period of time to be adsorbed by the substrate 107, and the purge gas is then introduced from the at least one purge gas introduction tube 104 for a predetermined period of time so as to purge the source gases remaining in the showerhead 106 and the chamber 101. Subsequently, the gases are discharged through the outlet 100. Thereafter, the reactant gases introduced through the at least one reactant gas introduction tube 103 are injected through the showerhead 106 onto the substrate 107 for a predetermined period of time, and consequently, a thin film is formed on the substrate through the predetermined reaction of the reactant gases with source gases adsorbed in the substrate 107. Further, before the source gases are injected again, the reactant gases and reaction byproduct gases remaining in the showerhead 106 and the chamber 101 are purged by using the purge gas for a predetermined period of time and then discharged. As described above, the thin film is deposited on the substrate 107 by repeating the processes of injecting and purging the source gases, and injecting and purging the reactant gases.
However, the technology using such a conventional chemical vapor deposition apparatus has a disadvantage of a very low deposition rate, and becomes a cause of increase in fabrication costs of a semiconductor when it is applied to a mass-production process of the semiconductor.
FIG. 1B is a schematic view showing a conventional plasma chemical vapor deposition apparatus in which the process gases are sequentially supplied and which is constructed to make up for the disadvantages of the chemical vapor deposition apparatus shown in FIG. 1A. That is, as shown in FIG. 1B, the conventional plasma chemical vapor deposition apparatus is constructed in such a manner that the showerhead 106 is provided with an RF power source connection portion 109 which in turn is connected to an external RF power source 110, and that an insulating portion 111 for electrically insulating the showerhead 106 to which the RF power source 110 has been connected is installed on the showerhead 106, thereby generating the plasma directly within the chamber 101.
That is, although the plasma chemical vapor deposition apparatus shown in FIG. 1B has a conventional sequential process gas supply system in which the processes of injecting and purging the source gases, and injecting and purging the reactant gases are repeated in the same way as the chemical vapor deposition apparatus shown in FIG. 1A, it is constructed to ensure a fast reaction rate at a lower temperature by directly generating the plasma directly within the chamber 101 upon injection of the reactant gases and inducing reactions of the plasma of the reactant gases with the source gases adsorbed in the substrate 107.
The direct plasma generating system shown in FIG. 1B ensures a slightly faster deposition rate at a relatively low temperature as compared with the system mentioned with reference to FIG. 1A. However, there is a disadvantage in that the substrate and circuit elements formed on the substrate may be damaged due to generation of arc at an initial stage of the plasma generation, ion bombarding and ion implant, and thus, the yield of the process is reduced.
FIG. 1C is a schematic view showing constitutional elements of a conventional chemical vapor deposition apparatus in which the process gases are sequentially supplied and an external plasma generating apparatus is employed. After the source gases are injected through the showerhead 106 for a predetermined period of time, the purge gas causes the source gases remaining in the showerhead 106 and the chamber 101 to be purged and discharged through the outlet 100 formed on a side of the chamber 101. After such purging of the source gases, the plasma of the reactant gases is injected through an external plasma generating apparatus 112 directly into the chamber 101 and the reactant gases are injected. Then, the reactant gases and the reaction byproduct gases are purged and discharged by using the purge gas.
In such a case that the chemical vapor deposition apparatus having the external plasma generating apparatus is utilized, it is possible to somewhat reduce the damage caused to the substrate and the circuit elements formed on the substrate due to the plasma. However, there is a disadvantage in that a thin film cannot be uniformly deposited on a substrate having a large area due to non-uniformity of the plasma introduced directly into the chamber.